This invention relates to plastic injection molding equipment, and in particular to a plastic injection nozzle having a trap which is easily purged of foreign contaminants.
In the plastic injection molding industry, regrind material is sometimes used for parts in which the external appearance or color is unimportant. Whenever such material is used for plastic injection molding, there is a risk of tramp metal or other contaminants lodging in the nozzle. This usually occurs in the tip area of the nozzle due to the restricted oriface size. The effect of a plugged nozzle is costly machine down time.
Previously, any time a nozzle became plugged, it was necessary to remove the nozzle for cleaning. At best, the removal of a nozzle is cumbersome because of the elevated temperatures, usually above 400.degree. F., and the presence of melted plastic. Often, heater bands and monitoring equipment must be removed prior to removal of the nozzle. This operation is usually beyond the capability of the basic machine operator. Even for experienced maintenance personnel, the removal of a nozzle requires at least 30 minutes.
The prior art discloses removable nozzle tips which can be used in a nozzle body. If a removable nozzle tip is used, the cleaning operation may then be done in about 15 or 20 minutes. However, this is still a complicated operation since hot plastic is involved, and considerable time must be spent in carefully handling the parts to avoid burns.
As an alternative to frequent nozzle removal, metal trap adaptors have been developed. The metal trap uses a filter disk to trap contaminants. Typically this would be an enclosed metal disk of approximately 1.75 inches in diameter with a plurality of small diameter holes across the face. This trap will effectively stop metal before it reaches the tip. It will also hold more contaminants than would be possible in a conventional tip before flow is affected. Nonetheless, cleaning still involves the same objections as given above in that the hot metal trap must be disassembled for cleaning.
In any of the above assemblies, it must be realized that the fluctuating temperatures encountered during the time required for the cleaning operation causes degradation of the plastic in the barrel of the molding machine. Thus, additional time and material is lost and further cleaning may be required as a result.
The prior art further discloses a metal trap of the type having a multiplicity of small holes which can be cleaned by turning a gate to allow the metal contaminants to flow on through the nozzle. However, when the cleaning process is attempted, the nozzle tip is still subject to becoming plugged by the contaminants released from the trap. In both of the above filter trap designs having a multiplicity of holes it is possible that a gradual blockage of the filter may occur. Thus the operator might not initially be aware that problems exist. Partial blockage results in higher pressures in the molding machine. Further, the plastic's speed may be dramatically increased through the remaining holes, leading to momentarily excessive heating and degradation of the plastic.
Accordingly, it is the general object of the present invention to provide a plastic injection nozzle having a trap which is easily purged of contaminants through a purge hole in the nozzle body.
Another object is to provide a rotatable housing in which the trap is located, which is rotatable from a first position where the plastic material flows through normally, to a second position in which the trap is purged.
Another object is to provide a trap which is very quick to clean, resulting in low machine down time and little degradation of the plastic material.
Yet another object is to provide a simple trap, where it is readily apparent to the operator that contaminants are blocking the nozzle.
A further object is to provide a nozzle which is tightly sealed in normal operation.
Another object is to provide a nozzle which is easily and quickly cleaned by the basic machine operator.
Another object is to provide a nozzle which is safe to clean of contaminants.
A still further object is to provide a color mixing nozzle tip for mixing the molten plastic after it has passed through the trap area.
These and other objects and advantages of the present invention and the manner in which they are achieved will become apparent in the following specification and claims.